Heat treatment of inlaid pressure vessels

ABSTRACT

A process to manufacture an oilfield component comprises selectively reinforcing a base material with an age-hardenable clad material and selectively heating at least a portion of the clad material such that it age-hardens and the base material remains at less than the tempering temperature of the base material. A body of a ram blowout preventer comprises, a low-ally base material, a vertical bore through the body and a horizontal bore through the body intersecting the vertical bore, wherein the body is heat treated by a process comprising selectively heating at least a portion of the clad material such that the clad material age-hardens and the base material remains at less than the tempering temperature of the base material.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit, pursuant to 35 U.S.C. §120,as a Continuation-In-Part application of U.S. patent application Ser.No. 11/555,984 filed on Nov. 2, 2006, and entitled “Heat TreatmentMethod of Inlaid Pressure Vessels,” which is expressly incorporated byreference in its entirety.

BACKGROUND OF INVENTION

1. Field of the Invention

Embodiments disclosed herein relate generally to oilfield components andequipment used during oil and gas production. Specifically, embodimentsdisclosed herein relate to a method of heat treating oilfieldcomponents.

2. Background

A variety of designs exist for the drilling and production ofhydrocarbons, including onshore and offshore drilling and productionunits. Offshore drilling and production unit designs may vary based uponwater depth and the type of platform used, such as floating platforms,semi-submersible platforms, tension leg platforms, spar-type platforms,and others as are known in the art. Offshore units also vary in the typeand location of control devices, including wet-tree systems, where thecontrol devices are located atop a wellhead on the sea floor, anddry-tree systems, where the control devices are located on the platform.

Components used during the drilling and production of oil wells,regardless of the location and design, are subject to corrosion, wear,and fatigue. For example, with respect to offshore drilling andproduction, components and equipment used are subject to a dynamicenvironment, where near-surface and sub-surface currents may impartbending, tension, and/or rotational stress. In a typical deepwateroffshore production, for example, a riser extends between a floatingplatform, at the surface of the ocean, and the wellhead, at the seafloor. Because the wellhead is statically located at the sea floor andthe riser and the platform or drilling rig are motive, the impartedstresses may fatigue production components, including buoyancy devices,stress-relief subs, pad-eye connections for ballast or tension lines,stress joints, blowout preventers (“BOPs”), well control assemblies, mudlift modules, ballast weights, and other components known in the artsEach of these components, including the connections at the platform, theriser joints, and the wellhead components, may experience stress andstrain associated with the dynamics of the offshore environment.

As another example of components subject to wear, corrosion, andfatigue, “rod” pumps are often used during the production of oil and gasfrom a reservoir. This deep well pump is mechanically activated by awalking beam pumping unit which is connected by one end to a powersource and by the other end to a string of steel rods (e.g., suckerrods) that interconnect themselves to form a string of rods extending tothe inside of the well, with the string connected by its other end tothe deep well pump. During pumping, the string of rods performs areciprocating or rotating movement, which may produce deflections of thestring. The sucker rods are thereby subjected to wear due to frictionalcontact with the inner wall of the production tubing. Even though thefluid environment serves as a lubricant, abrasion does occur over thesurface of the sucker rods. Additionally, tools used during assembly,such as those used for centering the string, may cause tearing of therod surface. In the case of hydrocarbon wells, the fluid includesdissolved salts and undissolved minerals which may have an additionalabrasive effect on the rod surface. At the same time that abrasionoccurs, the metal in the sucker rods is subjected to a hard corrosiveattack caused by downhole chemicals. These rods also experience veryhigh cyclic axial tension over their service life and may be subject toaxial fatigue.

In addition to the dynamic, abrasive, and corrosive stresses brieflydescribed above, oilfield components may also be subject to fatigue dueto the high pressures and temperatures encountered during the drillingand production process. The process of drilling wells involvespenetrating a variety of subsurface geologic structures, or layerscalled “formations.” Occasionally, a wellbore will penetrate a formationhaving a formation pressure substantially higher than the pressuremaintained in the wellbore. When this occurs, the well is said to have“taken a kick.” The pressure increase associated with the kick isgenerally produced by an influx of formation fluids (which may be aliquid, a gas, or a combination thereof) into the wellbore. Therelatively high pressure kick tends to propagate from a point of entryin the wellbore uphole (from a high pressure region to a low pressureregion). The normal operating pressures and the high pressure kickssubject the oilfield components to additional fatigue.

In the past, oilfield components subject to fatigue loading conditionswere manufactured from a single metallic alloy. The alloys normallyutilized are generally low-alloy steels processed by heat treatment tothe mechanical properties suited to the loading conditions. The use of ahigh strength nickel-based alloy in the manufacture of these parts wouldnormally be cost prohibitive.

In many cases, these oilfield components may need to meet the designcriteria for metallic oil and gas field components, such as thoserequirements established by NACE International (formerly the NationalAssociation of Corrosion Engineers) and the European Federation ofCorrosion for the performance of metals when exposed to variousenvironmental compositions, pH, temperature, and H₂S partial pressures.For example, NACE MR0175 limits the maximum hardness of the parts toRockwell C 22 or Brinell 237 for low-alloy steels in the quenched andtempered condition.

For most low-alloy steels, the maximum yield strength that they are ableto reach under the NACE maximum hardness limitation is about80,000-90,000 psi. Very few low-alloy steels are able to develop thisyield strength and hardness combination in a section thickness havingany useable significant size. For example, when the section thickness ismore than four to six inches, many low-alloy steels cannot develop thedesired mechanical properties on quench and temper throughout theirentire section thickness at the time of heat treatment.

Since fatigue life may be affected by the amount of stress imposed on amaterial relative to its yield strength, many materials exhibit ashorter life in fatigue when the stress applied exceeds as low as 50% ofits yield strength. Consequently, if the parts are used in fatigueloading conditions such as those defined in NACE MR0175, the allowableapplied stress may be limited to 50 to 65 ksi or less.

If fatigue failure occurs at these stress levels, there is little thatmay be done other than to reduce the applied stress by reducing the loadon the part. Because the mechanical strength of the alloy cannot beincreased significantly without exceeding the maximum hardness valuemandated by NACE MR0175, reducing the applied stress was the onlysolution formerly available. Furthermore, fatigue strength is dependenton ductility as well. Thus, because ductility and strength are inverselyrelated material properties, raising the strength of a material toaccommodate fatigue properties may be counterproductive.

Fatigue failure is a phenomenon that results from high tensile stress atthe surface or within close proximity to the surface of a material.Therefore, surface modification procedures, such as shot peening, casehardening by nitriding or carburizing, and flame hardening or inductionhardening, have been used to increase the fatigue strength of a materialby leaving a residual compressive stress at the surface. Parts thatcontain a residual compressive stress at their surface are less likelyto fail in fatigue since cracking is more difficult to initiate and/orpropagate when the part is residually loaded in compression.

While these surface modification procedures may aid in reducing oreliminating fatigue failures, shot peening and nitriding are superficialwhile carburizing and flame or induction hardening generally are notcapable of modifying the material properties to depths below the surfaceof more than approximately 0.050 inches. Furthermore, these surfacemodification methods may be at odds with or violate the requirements ofNACE MR0175 for use of the equipment in sour service or seawaterenvironments. For example, the hardness induced on the surface or nearsubsurface of a part may be in excess of the threshold value for sulfideor chloride stress corrosion cracking.

As mentioned above, the lifespan of an oilfield component may also beaffected by corrosion, such as by exposure to H₂S. For many years, partsin the oil tool industry have been clad overlaid on the ring grooves,sealing areas, and wetted surfaces solely for the prevention of damageto the base metal from the well bore fluid. For example, U.S. Pat. No.6,737,174 discloses a sucker rod having a surface coated by a copperalloy. In other clad overlay processes, a corrosion resistant alloy(“CRA”) clad layer, such as nickel based Alloy 625 (i.e., INCONEL 625)has been applied in thicknesses nominally from 0.060 to 0.187 inches toprotect a base metal from corrosive attack. Other CRAs may be used inthese applications, but the industry has essentially standardized Alloy625 for CRA cladding of oil tool equipment. There has been little if anyattention paid to the strength of the cladding material except to assurethat the strength of clad layer material is equal to or greater than thestrength of the base metal in the part.

Oilfield components and parts having an increased service life aredesired, including parts subject to high temperatures, corrosive fluids,high stress levels, and/or fatigue loading conditions, including cyclicloading conditions. Accordingly, there exists a need for oilfieldcomponents that have improved performance under various extremeoperating conditions, including fatigue loading conditions.

In the prior art, ram and annular BOP bodies, as well as accessoryequipment, have typically been manufactured for use in operatingpressures up to 15,000 psi and temperatures up to 250° F. These BOPbodies are manufactured using one-piece, rough machined, and heattreated low-alloy steel forgings or multiple piece low-alloy steelforgings that have been rough machined, heat treated and fabricationwelded together. Castings have been and still may be used for themanufacture of these ram BOP bodies for these service conditions as wellas forgings.

In the prior art, one-piece single, dual, or triple ram BOP bodies,which may be produced from low-alloy steel Grade F22, are quenched andfinal-tempered to meet the final material specification requirements.Alternatively, fabricated BOP bodies may be fabricated by weldingtogether low-alloy steel Grade 8630 Modified quenched and final-temperedparts. The bodies are then machined to near net shape and weld overlaidwith a corrosion resistant alloy, such as, AISI 316 austenitic stainlesssteel or nickel base Alloy 625 in the API ring grooves, bonnet faces andinternal top seal area and other areas designated on the engineeringdrawings.

After fabrication welding and/or overlay welding, the BOP bodies areconventionally given a post-weld heat treatment (“PVVHT”) at atemperature dependant on the steel grade from which the parts have beenproduced. The purpose of the PWHT is primarily to reduce the hardness ofthe heat affected zone (“TAZ”) of welded areas to the maximum hardnesslevels mandated by NACE MR0175 of HRC 22 or Brinell 237 for resistanceto sulfide stress corrosion cracking (“SCC”).

This PWHT is mandated by the controlling welding specification, ASMESection IX, to be performed at a temperature below the temperingtemperature of the base metal itself. The PWHT operation tends to reducethe mechanical properties of the base metal and limits the number oftimes that a particular BOP body can be welded and post-weld heattreated before the mechanical properties of the base metal have beendegraded to a level below the minimum requirements for the base metalrequired for the part. After the PWHT operation has been performed, thebodies are then finish machined to their final dimensionalconfiguration.

As detailed in the current disclosure, the prior art manufacturingprocedure may be changed to use a high strength, age hardenable,corrosion resistant alloy, CRA, to selectively reinforce areas of theone piece body for encapsulation of the high surface or near subsurfacestresses in the BOP body. This change may allow manufacture of BOPbodies for use at operating pressures above 15,000 psi and at operatingtemperatures up to 350° F. and above.

However, if the prior art method of manufacture were used, as describedabove, the PWHT temperature would be sufficient to obtain the requiredmaximum HAZ hardness value but the PWHT temperature would be too low toobtain the required mechanical properties in the age hardenable CRAoverlay material. If the PWHT temperature were increased to obtain themechanical properties in the CPA overlay material, the PWHT temperaturewould equal or surpass the tempering temperature of the Grade F22 basematerial of the BOP body, which is prohibited by ASME Section IX.

For example, where the CRA filler metal for the clad overlay welddeposition is INCONEL 725 and the base material is Grade F22 low-alloysteel, the Grade F22 steel must be post-weld heat treated at a minimumtemperature of 1150° F. (621° C.) for a period of time ranging from fourto eight hours or more. The Grade F22 low-alloy steel with sectionthickness of eight inches and greater will be quenched and tempered todevelop a minimum yield strength of 85,000 psi. To develop this minimumyield strength requires a tempering temperature of 1150° F. to 1250° F.(621° C. to 677° C.) for a period of time of eight to ten hours or more.However, since the INCONEL 725 is an age hardenable alloy, in order todevelop its mechanical properties on the order of 120,000 psi minimumyield strength, it must be aged at a temperature of 1200° F. (649° C.)for a minimum period of time of eight to twenty four hours. All of thesevarious tempering temperatures and times, PWHT temperatures and times,and the age hardening temperatures and times may be in conflict with oneanother.

If the base metal is conventionally quenched and final-tempered asdescribed above, the age hardening temperature and time for the INCONEL725 would further temper the Grade F22 base metal, likely lowering itsmechanical properties below the minimum specification requirement. Ifthe INCONEL 725 weldment joint on the Grade F22 were PWHT as describedabove, the maximum HAZ hardness would be met and the mechanicalproperties of the Grade F22 would be preserved, but the INCONEL 725 weldmetal would likely not develop the mechanical properties in the overlaythat are desired.

Accordingly, there exists a need for methods of manufacture to obtainparts meeting the requirements for HAZ hardness and mechanicalproperties for both the base metal and the clad overlay for use inoilfield service.

SUMMARY OF INVENTION

In one aspect, embodiments disclosed herein relate to a process tomanufacture an oilfield component comprising selectively reinforcing abase material with an age-hardenable clad material and selectivelyheating at least a portion of the clad material such that it age-hardensand the base material remains at less than the tempering temperature ofthe base material.

In another aspect, embodiments disclosed herein relate to a body of aram blowout preventer comprising a low-alloy base material, a verticalbore through the body, a horizontal bore through the body intersectingthe vertical bore, wherein at least a portion of the body is selectivelyreinforced with a clad material, and wherein the base material is heattreated by a process comprising selectively heating at least a portionof the clad material such that the clad material age-hardens and thebase material remains at less than the tempering temperature of the basematerial.

Other aspects and advantages will be apparent from the followingdescription and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is section view drawing of a flange neck reinforced in accordancewith embodiments disclosed herein.

FIG. 2 is a block diagram of a process to manufacture an oilfieldcomponent in accordance with embodiments disclosed herein.

FIGS. 3A and 3B are schematic drawings of a base material having variousconfigurations of a clad inlay.

FIGS. 4A and 4B compare simulation results for selective heat treatmentof a clad inlay with forced cooling and selective heat treatment of aclad inlay with natural convective cooling of the base material.

DETAILED DESCRIPTION

In one aspect, embodiments disclosed herein relate to a method ofmanufacturing or reinforcing oilfield components. In other aspects,embodiments disclosed herein relate to the heat treatment of oilfieldcomponents that have been selectively reinforced to reduce or eliminatestress and/or fatigue failures. In yet other aspects, embodimentsdisclosed herein relate to the selective heat treatment of theselectively reinforced areas of the oilfield components.

As used herein, “oilfield components” refer to flanges, bonnets, spools,stress joints, blowout preventers, sucker rods, subsea well assemblies,valves (e.g., choke valves), valve bodies, wellheads, and otherequipment and parts commonly used for the drilling and production of oiland gas. Those skilled in the art will recognize that, although notspecifically disclosed or described in detail, embodiments disclosedherein may apply to other oilfield components.

Component Design and Analysis

During transport, installation, and operation, oilfield componentsexperience stress and strain based on fatigue loading conditions, manyof which may occur on a continuous, semi-continuous, or cyclic basis.Loading conditions may include thermal loading, pressure loading, ormechanical loading. For example, thermal loading may occur when awellbore is hot (e.g., 300° F.) and is located in 10,000 feet of waterat 32° F. Pressure loading may result from internal (wellbore) pressureacting outward on the oilfield component or from hydrostatic (e.g.,subsea) external pressure acting inward, Further, mechanical loading mayinclude bonnet and flange bolt tightening preloads, axial tensile andcompressive loads, and bending moments. As such, the loading conditionsmay include at least one of internal pressure, external pressure, axialtension, axial compression, longitudinal tension, longitudinalcompression, axial bending moment, longitudinal bending moment, risertension and bending, and temperature extremes, among other load states.The intensities of the local stress states placed on the equipmentduring these loading conditions may have a significant impact on thecyclic life of the equipment. Analyzing the performance of an oilfieldcomponent subject to various fatigue loading conditions may provide forenhancing the design and/or improving the performance of the oilfieldcomponents to extend the useful life of the oilfield component.

Finite element analysis (“FEA”) is a useful and powerful technique foranalyzing stresses and strains in structures or components too complexto analyze by strictly analytical methods. With FEA, the structure orcomponent is broken down into many small pieces (a finite number ofelements) of various types, sizes and shapes. The elements are assumedto have a simplified pattern of deformation (linear, quadratic, etc.)and are connected at “nodes” normally located at corners or edges of theelements. The elements are then assembled mathematically using basicrules of structural mechanics, i.e., equilibrium of forces andcontinuity of loads, resulting in a large system of simultaneousequations (a mesh).

By solving this large simultaneous equation system with the help of acomputer, the deformed shape of the structure or component under loadmay be obtained, from which stresses and strains may be calculated.Suitable software to perform such FEA includes ABAQUS (available fromABAQUS, Inc.), MARC and PATRAN (available from MSC SoftwareCorporation), and ANSYS (available from ANSYS, Inc.), among others.Finite elements of any shape known in the art may be used. Hexagonalelements, though, are typically highly stable and may be beneficial whensimulating high stresses and strains across a model.

A simplified design and/or model of an oilfield component to assist inthe analysis of the oilfield component may be used. For example, theanalysis of stress and strain concentrations of complex componentdesigns may be simplified by “smoothing” that design. As used herein,the term “smoothing” refers to various techniques to simplify a complexgeometry of a design for use with FEA. For example, internal corners maybe modified to reduce or eliminate their radii in an attempt to simplifya subsequently constructed model. These techniques may allow theanalysis of a smoothed model (i.e., an FEA model constructed from asmoothed design) to correlate and converge to a definitive result whenanalysis of a non-smoothed model may not. As such, a model constructedfrom a smoothed design may be analyzed with FEA to determine an overall,or bulk, stress condition. By analyzing the bulk stress, theperformance, and possible failure, of an oilfield component undervarious fatigue loading conditions may be predicted.

One objective of FEA may be to isolate high stress or strain areas andidentify the areas that are prone to low cyclic life. The results of afinite element analysis, analyzing the performance of the componentunder various fatigue loading conditions, may be used to identifyregions subject to fatigue failure in the oilfield component. Once theregions subject to fatigue failure are identified, these areas may bere-designed or may be marked for metallurgical processing, such asselective reinforcement, as will be described later.

Possible load states or fatigue loading conditions for the componentshould be determined for input into the FEA. As mentioned above, thesemay include normal operating pressure, high-pressure kick, riser tensionand bending, and temperature extremes, among other load states. Thefatigue loading condition data should include typical or expected valuesas well as maximum and/or minimum values and the frequency at whichthese loads fluctuate to enable a complete analysis.

Properties of the base material used to form the oilfield componentshould also be determined, establishing the maximum allowable peakstress value (SBpeak). The material properties may either be determinedthrough empirical testing or, in the alternative, may be provided fromcommercially available material properties data. For example, this valuemay be established based on field tests where, under NACE environments(i.e., environments established by NACE International for testing of oiland gas field equipment), the stress would just meet the life cyclerequirement and would be less than the stress at which sulfide stresscorrosion cracking would occur.

More particularly, the tensile properties of the base materials may bedetermined. The tensile strength of a material is the maximum amount ofstress (in tension) a material may be subjected to before failure. Asstress is exerted upon a material, the material strains to accommodatethe stress. Once the stress is too much for the material, it will nolonger be able to strain, and the material fails. The failure point ofthe material is known as the ultimate tensile strength.

The loading conditions and material properties may then be used toanalyze the oilfield component using FEA based methods. All permutationsfor design and operating loads should be considered to generate acomplete analysis of the component. Proper bolt preloads and materialcharacteristic data, de-rated based on temperature, should also be used.

A model (i.e., a mesh of simultaneous equations) for the oilfieldcomponent is generated for use in the finite element analyses. Athree-dimensional model of the component may be generated with specificdesign features. These design features may be selected to give specificperformance characteristics. Thus, generating a model may also includethe steps of importing a component design to generate the model andsmoothing the imported design. The design may have various smoothingtechniques applied thereto to simplify FEA analysis. The models may begenerated from a design in a computer aided design (“CAD”) softwarepackage (e.g., AutoCAD available from Autodesk, Inc., and Pro/Engineeravailable from Parametric Technology Corporation) and imported into theFEA software package. Alternatively, the model may be generated withinthe FEA packages (e.g., ABAQUS and PATRAN) themselves.

Next, the loading conditions may be simulated upon the component in FEAusing the model. Preferably, these simulated fatigue loading conditionsreflect the load states or stress that the oilfield component may expectto experience under normal use. Further, after simulating fatigueloading conditions upon the model, a stress plot from the loadingconditions showing the stress and deformation occurring in the oilfieldcomponent model may be analyzed. The stress plot may determine and showthe location and amount of stress occurring in the oilfield componentmodel from the simulated loading conditions across the component.

The stress plot may be analyzed and reviewed to determine theperformance and characteristics of the model. If the model may befurther improved, another model may be generated or the current modelmay be re-generated (modified). This will allow the model to be furthersimulated in FEA to determine its performance after furthermodifications or models. Otherwise, if the model is consideredacceptable and meets any and/or all specified criteria, the model may beused in the manufacture oilfield components, as will be described below.

Selective Reinforcement

Objectives of the numerical methods (e.g., FEA analysis) includeidentifying, isolating, and highlighting zones subject to fatiguefailure within the oilfield components. For example, the stress stateswhich may cause early failure under NACE environment may be identified.The results of the FEA may be used to generate stress and strain plotsfor identifying regions subject to fatigue failure in the component.

The identified zones subject to fatigue failure may be modified in themanufacture of the oilfield component. For example, the zones may bemarked out, in a spatial representation or drawing, noting the depth andlateral extents (length and width) of high stress areas subject tofatigue failure. A contour plot may be drawn, showing the length, width,and depth of the local stress areas. The surface location of the fatiguezones, for example, may be transferred to appropriate manufacturer'sdrawings. The identified fatigue zones may then be selectivelyreinforced with a higher strength material bonding metallurgically withthe base material.

It may be possible, in some embodiments, to reduce or help preventfatigue failure by surface substitution methods. For example, if somedepth of the part base metal of low-alloy steel is removed and replacedwith a higher strength material and a metallurgical bond with the basemetal is developed, fatigue failures may be reduced or eliminated. Thehigher strength alloy may be any convenient alloy of the user's choosingthat exhibits the strength, ductility, and corrosion resistance requiredby the design of the oilfield components or parts.

The higher strength material may include other low-alloy or medium-alloysteels with higher strength and/or higher corrosion resistance than thelow-alloy steel base metal and would be capable of withstanding theapplied stresses with a lower ratio of applied stress to yield strength.Lowering the ratio of applied stress to yield strength of the higherstrength material would reduce its tendency to initiate fatiguecracking, fatigue crack propagation and ultimate fatigue failure. Forexample, a high strength alloy such as Alloy 625 may be used to replaceand bond with the low-alloy base metal. The choice of the cladding alloythat could be substituted for the partial thickness of the base metalsubstrate up to 0.500 inches or more would be made on the basis of theratio of the applied stress to the yield strength of the alloy used forthe clad layer.

In some embodiments, the base material may be selectively reinforcedwith an inlay clad. In other embodiments, the base material may beselectively reinforced with an overlay clad. The clad inlay or overlaymay be bonded to the base material using pressure, heat, welding,brazing, roll bonding, explosive bonding, weld overlaying, wallpapering,or a combination thereof. In some embodiments, the cladding may bebonded to the base material using an electric arc welding process, suchas a submerged arc welding (“SAW”) process or a tungsten inert gas(“TIG”) welding process. In other embodiments, the cladding may bebonded to the base material using an electric arc weld cladding process,a hot isostatic pressing cladding process (“HIP” cladding),auto-frettage cladding, laser cladding, or a combination of any of thesemethods. In some embodiments, one or more clad layers may be used, suchas a single clad having two layers (base plus clad), a double clad(having 3 layers), or a cladding of up to 7 or more layers.

In some embodiments, the base material may be selectively reinforcedwith a clad inlay. The clad inlay, in various embodiments, may beshrunk-fit or press fit into recesses cut in the body of the oilfieldcomponent, and seam/seal welded in place. In other embodiments, the cladinlay may be shaped according to the FEA stress plots.

The clad inlay or overlay, in some embodiments, may have a thickness oran average thickness of up to 0.625 inches or higher. In otherembodiments, the clad inlay may have an average thickness in the rangefrom about 0.010 inches to about 0.625 inches; from about 0.050 to about0.500 inches in other embodiments; and from about 0.125 to about 0.375inches in yet other embodiments.

In other embodiments, press-fit or shrink-fit component partsmanufactured of the high-strength alloy may be used in conjunction withthe oilfield components. For example, solid parts (e.g., flanges,bonnets, valve bodies, etc.) made of a high-strength alloy (e.g.,INCONEL 725) may be seal welded to a low-strength substrate after beingpressed or shrunk-fit into a body.

In other embodiments, the base metals in the identified fatigue zonesmay be replaced with a higher strength material bonding metallurgicallyto the base material. For example, the base metals in the high stressareas may be ground or machined away and replaced with a higher strengthmaterial bonding metallurgically to the base material.

In some embodiments, the selective reinforcement is a clad overlay ofhigher strength material over a base material. In other embodiments, theselective reinforcement may be a clad overlay of higher strengthmaterial in ground or machined recesses in a base material.

The choice of the cladding alloy may be based on its ability to resistcorrosion, including stress corrosion cracking, and its ability to addmechanical strength (e.g., by a metallurgical bond to the low-alloysubstrate) to the portion of the oilfield component to which it isapplied and intended to protect. In a typical overlay, for example, thestrength of the cladding material is expected to at least equal thestrength of the base metal to which it is applied. That is, the welddeposited alloy (such as Alloy 625) is expected to match the yieldstrength of the low-alloy steel base metal (such as low-alloy steelhaving a yield strength of 75,000 psi). It may be possible to apply acladding of a higher strength material in a thickness that willencapsulate the localized stresses in the higher strength clad layer,resulting in an oilfield component that will meet NACE or otherstandards for oil and gas field components and equipment while meetingthe strength and fatigue requirements of the design.

In some embodiments, the base material may be F22 low-alloy steel, asteel having approximately 2 weight percent chromium and 1 weightpercent molybdenum. Alternatively, the base material may be 4130 or 8630modified low-alloy steel. Those skilled in the art will recognize thatother materials, having appropriate corrosion resistance, hardness, andtensile properties suitable for use in an oil and gas environment, mayalso be used as a base material.

In some embodiments, the clad overlay or clad inlay may be formed fromhigh yield strength, precipitation-hardenable corrosion resistantalloys, such as INCONEL 725, or INCONEL 725 NDUR, for example. In otherembodiments, the clad overlay or clad inlay may be formed from highyield strength, precipitation-hardenable corrosion-resistant alloys suchas Alloy 718 or INCONEL 718 SPF. In still other embodiments, the cladoverlay or clad inlay may be formed from other precipitation-hardenablecorrosion-resistant alloys such as 17-4PH, INCONEL 625 or INCOLOY 925.Those skilled in the art will recognize that other high strengthcorrosion resistant materials may also be used as a cladding.Preferably, the cladding material is compatible with the base materialand is a precipitation-hardenable alloy.

The alloys for use as a cladding may be available in the form of weldwire, powder, or strip filler metal for weld cladding and may also beavailable in the form of a powder intended to be used in a HIP claddingoperation. These alloys may also be available in other forms that may beused in an auto-frettage cladding operation.

Once the cladding method or combination of cladding methods has beenchosen, the minimum thickness and locations of the clad layer may bedetermined based on the results of the FEA stress analysis. The requiredthickness or depth of the cladding may vary depending upon the alloyused in forming the cladding, the bond formed between the clad and thebase materials, as well as the dilution of the clad material resultingfrom the process used to bond the clad material to the base material.Once the values and location of the areas subject to fatigue failurehave been determined, the cladding alloy may be chosen. It may not benecessary to clad the entire oilfield component. Particularly, onlyportions of the component may need to be clad. Furthermore, it may bepossible to selectively place a much lower clad thickness in lowerstressed areas, thus preventing corrosion of those areas subject tocontact with the wellbore fluid.

As one example, referring now to FIG. 1, a schematic drawing of a flangeneck reinforced for fatigue control is illustrated. A vessel body 10 isattached to an integral flange 12 by flange neck 14. Flange neck 14 mayexperience fatigue loading conditions due to the movement of componentsattached to flange 12, due to the tensioning of the bolts in bolt holes16, internal pressure pushing outward on the vessel body 10 due to afluid in bore 18, and other loading conditions. The outer diametersurface 20 of flange neck 14 and the inner diameter surface 22 of vessel10 across the wall thickness from the flange neck 14 are commonlysubjected to high fatigue loading conditions, and may be selectivelyreinforced using clad inlays or clad overlays 24, 26, by the methodsdescribed above. For example, a flange neck subjected to fatigue loadingconditions is the bottom flange on ram and annular blowout preventerbodies used in a subsea wellhead assembly stack. These ram and annularblowout preventer bodies in the stack are subject to considerable cyclicbending loads which result in a severe bending fatigue situation on theflange necks. Selective reinforcement may additionally provide greaterresistance to stress corrosion cracking to these areas that are subjectto fatigue loading conditions.

As another example, drilling or production riser stress joints may beselectively reinforced to reduce or eliminate fatigue failures. Thisstress joint has in the past been manufactured from a high strengthtitanium alloy which is capable of withstanding much more bendingdeflection than a low-alloy steel because of the much lower modulus ofthe titanium alloy compared to the low-alloy steel. However, titaniumcomponents are very expensive and are not characterized by “fatiguestrength.” While steel components exhibit a fatigue strength, underwhich a component will not fail, regardless of the number of cycles,titanium components will eventually fail regardless of the magnitude ofthe cyclic loading. Therefore, by selectively reinforcing a low-alloysteel, it may be possible to manufacture a stress joint capable ofwithstanding the bending and deflection associated with the stress jointfor longer times (i.e., more cycles) using a lower cost material.

As another example, sucker rods and other components of rod pumpssubject to high cyclic axial fatigue may be selectively reinforced toreduce or eliminate fatigue failures. The use of a high strength surfacelayer on the OD surface of sucker rods, for example, may prolong theservice life of these parts as well. Moreover, a high strength corrosionresistant material would likely reduce the effects of any corrosionfatigue induced from the environment in which they are used.

As another example, valve bodies may be selectively reinforced to reduceor eliminate fatigue failures, to reduce or eliminate corrosion, and/orto be manufactured more economically. In the case of certain valves(e.g., choke valves), the selective reinforcing may also reduce oreliminate erosion caused by the high velocity flows on the downstream(i.e., the low-pressure) side of the choke valve.

As another example, blowout preventer bodies, in addition to the flangenecks, may also be subject to fatigue and may be selectively reinforcedto reduce or eliminate fatigue failures. As described above, blowoutpreventers are installed to limit the equipment that may be affected bya high pressure kick. There are several types of blowout preventers, themost common of which are ram blowout preventers and annular blowoutpreventers (including spherical blowout preventers). Ram blowoutpreventers, for instance, are currently manufactured in various boresize ranges, and may have a working pressure range from 2,000 to 15,000psi. However, it may be desired to use ram blowout preventers at higherpressure and higher temperature conditions (above 15,000 psi and greaterthan 250° F.). Particularly, ram blowout preventers rated at workingpressures of 20,000 psi, 25,000 psi, and higher and working temperaturesof up to 350° F. or higher, may be desired. For example, see U.S. patentapplication Ser. No. 11/528,873 titled “Reinforcement of IrregularPressure Vessels” by Huff and Khandoker, filed on Sep. 28, 2006, herebyincorporated by reference in its entirety. Results of the abovedescribed FEA for blowout preventers used under high temperature and/orhigh pressure conditions indicate that selective reinforcement ofvarious sections of the blowout preventer, such as the choke and killpockets, may enable the blowout preventer to be used at the highertemperatures and pressures.

The objectives of the above described numerical methods (FEA analysis)include identifying, isolating, and highlighting zones of high or peakstress (SBpeak) states within the BOP equipment. For example, the stressstates which may cause early failure under NACE environment may beidentified. The results of the BOP FEA may be used to generate stressand strain plots for identifying regions of high stress concentrationsin the vessel.

In addition, stress and strain plots may be used to define a criticalsection thickness (“CST”) in a casting or forging used in an oilfieldcomponent in order to accurately determine the appropriate heattreatment time at a selected temperature. Critical Section Thickness isdefined as the largest thickness of a component which must have certainminimum mechanical properties through the entire thickness. For example,a lightly stressed, thick walled portion of a pressure vessel or BOP maynot require 80,000 psi yield strength through its entire thickness, buta thinner portion may require 80,000 psi yield strength through theentire thickness in that portion; in this example, the thinner portionmay have the CST. A total heat treatment time may comprise a first time(expressed in minutes per inch of CST) and a second time (expressed inhours) which are summed together. For the purpose of this disclosure,the first time is called the “dwell” time and the second time is calledthe “soak” time. For example, a typical conventional heat treatment timemay include 30 minutes per inch of CST dwell time and one hour soaktime. In this example, a forging used in an oilfield component with aCST of 10 inches would require 6 hours heat treatment time at a selectedtemperature (i.e., 10 inches×30 minutes per inch dwell time plus 1 hoursoak time).

Furthermore, stress and strain plots may be used to isolate areas wherestresses exceed a selected percentage of base material yield strength.For example, in particular alloys used as a base material, areas inexcess of 80% yield may not pass NACE requirements (as discussed below),or may not provide an adequate engineering safety factor in a particularapplication, for example, operation at a particular combination ofinternal pressure and temperature. For example, areas in a BOP wherestresses may exceed a selected percentage of base material yieldstrength include seat pockets, the BOP pocket near the bonnet, and BOPinner bores (vertical bores, horizontal bores, and the intersections ofthe vertical and horizontal bores). These stress and strain plots mayalso be used to calculate the depth of the high stress zones in excessof a selected percentage of base material yield strength.

The identified high stress zones may be modified in the manufacture of aBOP. For example, the zones may be marked out, in a spatialrepresentation or drawing, noting the depth and lateral extents (lengthand width) of high stress areas exceeding the allowable SBpeak stress. Acontour plot may be drawn, showing the length, width and depth of thelocal stress areas in excess of a selected percentage of the basematerial yield strength. The surface location of the peak stress zones,for example, may be transferred to appropriate manufacturer's drawings.The identified high stress zones may then be selectively reinforced witha higher strength material. In some embodiments, this higher strengthreinforcing material may be metallurgically bonded with the basematerial.

Hardening

Selectively reinforced oilfield components, including flange necks,blowout preventers, sucker rods, and other components, particularlythose exposed to corrosive fluids, may need to meet the design criteriafor metallic oil and gas field components, such as those requirementsestablished by NACE International (formerly the National Association ofCorrosion Engineers) and the European Federation of Corrosion for theperformance of metals when exposed to various environmentalcompositions, pH, temperatures, and H₂S partial pressures (includingNACE MR0175, NACE TM0177, and NACE TM0284). For example, NACE MR0175limits the maximum hardness of the parts to Rockwell C 22 or Brinell 237for low-alloy steels in the quenched and tempered condition. Thesehardness limitations must be met in addition to developing the desiredyield strength for the selectively reinforced areas.

However, meeting the hardness limitation while developing the desiredyield strength may require changes to the current manufacturingtechniques. Post-weld heat treatment temperatures and times may be inconflict with the age hardening temperatures and times. For example,where a low-alloy steel base material is selectively reinforced with anickel-based corrosion resistant alloy (CRA), the post-weld heattreatment temperature may be sufficient to obtain the required maximumhardness value for the heat affected zone during welding of the cladoverlay, but the PWHT temperature may be too low to obtain the requiredmechanical properties in the age-hardenable CRA overlay material.

To overcome these competing temperature and time requirements, a methodof manufacturing the selectively reinforced oilfield components has beendeveloped to procure the desired properties in the base material and thematerial used to selectively reinforce the base material. In one suchmethod, a casting, forging, or hot isotactic pressing used in anoilfield component may be made from a base material including, but notlimited to, low-alloy steel. Appropriate low-alloy steels may include,but are not limited to, 4130, 8630 Modified, and F22.

The base material may then be normalized. For example, an F22 low-alloysteel forging may be normalized at 1750° F. for 30 minutes per inch ofthickness plus one hour. If desired, the castings, forgings, or hotisotactic pressings may then also be rough machined into a desiredconfiguration.

Following normalization, the castings, forgings, or hot isotacticpressings may then be quenched and snap-tempered (“Q&ST”) to preventcracking. As used herein, “snap tempering” describes an intermediate lowtemperature heat treatment that softens the alloy slightly and decreasesthe likelihood of cracking, especially so-called “autogenous” or “self”cracking. For example, a component made from F22 may be Q&ST to900-1000° F. for a dwell time of about 30 minutes per hour per inch ofCST, plus a soak time of one hour. Optionally, the rough machiningdescribed above may be performed after the snap tempering. As-forged,as-cast, and as-pressed components may be especially delicate and snaptempering after quench may allow them to be handled, shipped, and/orfurther machined without cracking.

Ordinarily, in conventional practice, castings, forgings, and pressingsused in oilfield components would be fully heat-treated by processesincluding normalizing, austenitizing, solution annealing, tempering,age-hardening, heat treating, and other methods as known in the art toachieve the desired final material properties before they are inlaid oroverlaid with CRA material. For example, according to conventionalpractice, a BOP body made from a low-alloy steel such as, for example,4130, 8630, or F22, would be fully heat treated and at least partiallymachined before it was weld-inlaid with a CRA material such as INCONEL625 in, for example, the ring gasket grooves on its flanged connections.In conventional practice, such an inlaid BOP body would then bestress-relieved (that is, annealed) to some temperature below thetempering temperature of the base material to ensure that the yieldstrength of the base material is preserved.

According to the current disclosure, the castings, forgings, andpressings used in oilfield equipment, having undergone Q&ST, may befinish-machined and selectively reinforced (as described above) with aclad material without fully tempering the castings, forgings, orpressings. Once selectively reinforced, the clad material may befinish-machined (if necessary) to obtain their final geometry.Furthermore, following selective reinforcement, the oilfield componentmay then undergo a single heat treating step, referred to herein as a“finish temper,” for a selected period of time at a selectedtemperature. In one embodiment, the selected period of time isintermediate a time required to completely temper the base material anda time required to age-harden the clad material. Furthermore, theselected finish temper may provide for one or more of (a) developing therequired mechanical properties of the base material, (b) post-weld heattreatment of a heat affected zone of a welded joint between the basematerial and the clad material, and (c) age hardening (also known as“precipitation hardening”) the clad material.

In another embodiment, the clad material may be further strengthened bya “supplemental heat treatment” after the finish tempering by theselective application of heat. For example, ceramic electric heatingblankets well known in the art may be used to “supplementally age” theclad material. In an exemplary embodiment of supplemental aging of theclad material, heat is applied to the surface of the clad material withceramic electric heating blankets so that a temperature gradient isdeveloped across the cladding material and the base material, such thatthe temperature of the base material is always less than the finishtempering temperature (or, in particular, less than the finish temperingtemperature minus about 50-100° F.).

In another embodiment, age-hardenable clad material may be applied asselective reinforcement to a conventionally quenched and final-temperedoilfield component (as discussed below), then the cladding may be“supplementally aged” as above without affecting the “final” temper.

In some embodiments, the finish-temper process is facilitated by a nexusbetween the tempering temperature of the base material and theage-hardening temperature of the clad material. In some embodiments, thebase material may have a tempering temperature within 100° F. of anaging temperature of the clad material. In other embodiments, there maybe as few as 75° F. or 50° F. separating the two temperatures.

Thus, in some embodiments, the time required by both the desiredtempering cycle and the desired age-hardening cycle are such that theymay coincide at a total finish temper time (dwell time plus soak time),achieving the properties required of both the base material and the cladmaterial. In other embodiments, the time required by both the temperingcycle and the age hardening cycle are such that a total finish tempertime intermediate a desired tempering time and a desired age-hardeningtime may achieve the properties required of both the base material andthe clad material.

The finish temper, as mentioned above, may result in the desiredproperties for both the base material and the clad material. In someembodiments, the finish temper may result in the base materialdeveloping a yield strength of between 80 ksi and 95 ksi. In otherembodiments, the finish temper may result in the clad materialdeveloping a yield strength of at least 115 ksi. In yet otherembodiments, the finish temper may result in an oilfield component witha base material having a maximum hardness of HRC 22 or Brinell 237. Inselected embodiments, these properties are met for each component.

In some embodiments, the finish temper temperature may be between about1200° F. to about 1300° F.; between about 1225° F. and 1300° F. in otherembodiments; and between 1215° F. and 1225° F. in yet other embodiments.In some embodiments, the finish temper temperature may be greater than apost-weld heat treatment temperature of the base material.

In some embodiments, the finish temper time of the selectivelyreinforced oilfield component may be 30 to 60 minutes per inch of CST“dwell” time plus one to two hours “soak” time. In other embodiments,the finish temper time for the selectively reinforced component may be30 to 45 minutes per inch of CST “dwell” time plus one to two hours“soak” time. In still other embodiments, the finish temper time may be38 to 42 minutes per inch of CST “dwell” time plus about one hour “soak”time.

As described above, embodiments disclosed herein may provide a methodfor manufacturing a selectively reinforced oilfield component. Theoilfield component may include a base material selectively reinforcedwith a clad material, and the method may include finish tempering theoilfield component at a selected time and temperature to temper the basematerial and age harden the clad material.

Referring now to FIG. 2, a block diagram of a process for manufacturinga selectively reinforced oilfield component in accordance withembodiments disclosed herein is illustrated. Manufacturing process 50may include step 52, providing a base material for an oilfieldcomponent. As one of ordinary skill in the art should understand,providing 52 may include, but is not limited to, forging or casting, hotisotactic pressing, rough machining of the base material, andnormalizing the base material. Next, manufacturing process 50 mayinclude quenching and snap tempering (Q&ST) 56 of the treated basematerial. Following snap tempering 56, the base material may beselectively reinforced 58 with a clad material. Selective reinforcing 58may include, for example, inlaying the base material with a corrosionresistant alloy, where the corrosion resistant alloy may have a higherstrength than the base material. After selectively reinforcing 58, theoilfleld component (i.e., the base material and the clad material) mayundergo finish temper 60. Finish temper 60 may include finish temperingthe oilfield component at a selected time and temperature to temper thebase material and age harden the clad material.

Supplemental Age-Hardening

As described above, the clad material may be supplementally age-hardenedto increase the yield strength of the clad material. Supplementalage-hardening may achieve the properties required of both the basematerial and the clad material. Heat may be selectively applied to atleast a portion of the clad material, and in some embodiments the cladmaterial may develop a yield strength of at least 115 ksi while the basematerial hardness remains Brinell 237 or less.

Supplemental age-hardening may be performed on a selectively reinforcedQ&ST oilfield component in some embodiments. For example, as describedabove, the castings, forgings, and pressings used in oilfield equipment,having undergone Q&ST, may be finish-machined, selectively reinforcedwithout fully tempering the castings, forgings, or pressings, and thenfinish tempered for a selected period of time at a selected temperature.The finish tempered oilfield component may then undergo supplementalage-hardening to further strengthen the clad material without furthertempering the base material.

Supplemental age-hardening may also be performed on a conventionallyquenched and final-tempered oilfield component. Castings, forgings, andpressings used in oilfield components may be fully heat-treated byprocesses including normalizing, austenitizing, solution annealing,tempering, age-hardening, heat treating, and other methods as known inthe art to achieve the desired final base material properties beforethey are inlaid or overlaid with CRA material. The conventionallyquenched and final-tempered oilfield component may then besupplementally aged to further strengthen the clad material withoutaffecting the “final” temper.

During supplemental age-hardening, at least a portion of the oilfieldcomponent may be actively cooled, thereby maintaining the base materialat a temperature less than a tempering temperature of the base material.As used herein, “active cooling” may include conductive cooling, forcedconvective cooling, heat exchange with a medium such as a moving fluid(vapor or liquid), spray cooling (e.g., a water spray on a portion ofthe surface), or other means of cooling known to those of skill in theart, exclusive of natural convective or still-air cooling. Activecooling may be used, for instance, where the age-hardening temperatureof the clad material exceeds the tempering temperature of the basematerial.

In some embodiments, the base material may remain at least 50° F. belowa tempering temperature of the base material during the selectiveage-hardening of the clad material; at least 75° F. below in otherembodiments; and at least 100° F. below in other embodiments.

Additionally, selective reinforcement of an oilfield component may notresult in a uniform thickness of clad material over an entire surface.In some embodiments, the thickness of the clad material may vary. Forexample, as illustrated in FIG. 3A, a selective reinforcement may beapplied where a portion of the clad material 30 is thick, tapering offto a minimal thickness at a surface interface 32 of the base material 34with the clad material 30. In other embodiments, a selectivereinforcement may be applied where the clad material 30 has a uniform ornearly uniform thickness, even at the interface 32 with base material34, as illustrated in FIG. 3B.

Where the clad material is supplementally aged, selectively heating theentire surface of the clad material may result in the base material, ator near the interface 32, exceeding the tempering temperature of thebase material. To avoid exceeding the tempering temperature of the basematerial at or near the interface, supplemental age-hardening mayinclude the selective heating of only a portion of the clad inlay. Forexample, as illustrated in FIG. 3B, the central portion 36 of clad inlay30 may be selectively heated, where conduction may age-harden the outerportions of the clad material 30 while maintaining the temperature ofthe base material 34 at or near interface 32 below a temperingtemperature of the base material 34. In this manner, the base material34, even at the interface 32 with clad material 30, may remain at ahardness of Brinell 237 or less.

Referring now to FIGS. 4A and 4B, results of FEA simulations performedto investigate the differences between active cooling and still-aircooling of a clad inlay during a supplemental age-hardening process areshown. In this example, FEA simulations were performed on a 12 inchthick, 19 inch inner diameter cylinder of F22 having a clad inlay of 0.5inch INCONEL 725 applied to its inner diameter. To simplify the model, auniform inlay thickness was assumed. The surface of the clad inlay wasset at 1350° F., and the temperature of the outer surface of thecylinder was varied based upon active cooling and still-air cooling.

As shown in FIGS. 4A and 4B, still-air cooling may result in an outerwall temperature of about 800° F., whereas active cooling may maintainthe outer wall temperature as low as 75° F. More importantly, activecooling may maintain the base material, at the interface with the cladmaterial (0.5 inch depth), at a temperature less than the temperingtemperature of the base material, 1180° F. In contrast, still-aircooling resulted in the base material exceeding the temperingtemperature. These simulation results indicate that active cooling mayprovide a method to supplementally age harden a clad inlay, whilemaintaining the base material at a temperature below the temperingtemperature of the base material.

In selected embodiments, during supplemental age-hardening, at least aportion of the clad material may be selectively heated to a temperaturebetween about 1250° F. and 1400° F. In some embodiments, duringsupplemental age-hardening, at least a portion of a surface of theoilfield component may be maintained at a temperature of 250° F. orless; 200° F. or less in other embodiments; 150° F. or less in otherembodiments; 100° F. or less in other embodiments; 75° F. or less inother embodiments; and 50° F. or less in yet other embodiments.

Exemplary Embodiments

The prior art manufacturing process described above may be modified inaccordance with the present disclosure as follows. The ram BOP body maybe forged and rough machined in the same manner as is presently done,however the heat treatment of the rough machined BOP body would bemodified. The body would still be normalized and austenitized at theappropriate temperatures and liquid quenched as is the present practice.After the completion of the liquid quench, the temper would be modifiedto a much lower value, and a “snap” or intermediate low temperaturetemper would be performed. As previously discussed, one purpose of thesnap temper is to prevent spontaneous or “autogenous” cracking of the asquenched low-alloy steel material during processing until the time ofthe final temper.

Upon receipt of the rough machined and snap-temper heat treated forging,the BOP body may be prepared for weld overlay. The BOP body may then beoverlay welded to selectively reinforce those areas determined by thestress analysis described above, which may be transferred to theengineering drawing. After all welding has been completed, the BOP bodymay be charged to the tempering furnace for finish tempering, acombination heat treatment of the weldment joint of the overlay cladmaterial on the low-alloy steel substrate.

The finish temper would consist of a temper for the base metal todevelop the mechanical properties required of the base metal by thematerial specification. The temper would also provide for the PWHT ofthe HAZ of the weldment joint since the tempering/aging temperaturewould be above the PWHT temperature normally used for the basematerial/CRA weldment joint. And lastly the temper would serve as theage hardening heat treatment for the high strength CRA overlay fillermetal.

This finish temper process is possible since the tempering temperatureof the base metal and the aging temperature of the CRA overlay materialmay be nearly identical, such as when the base material and CRA overlayare properly selected and processed. The time required by both thetempering cycle and the age hardening cycle are such that they may beaveraged and achieve the properties required of both materials.

The mechanical properties of the alloy may be determined by use of aseparate qualification test coupon, QTC, which may be heat treatedseparately from the part itself provided that it is heat treatedaccording to specific rules mandated by API for parts to be used in theoil exploration and production industry. For example, to verify that theBOP body conforms to the material property requirements, twoqualification test coupons, QTCs, may be produced from the same heat ofsteel from which the BOP body is produced. The two qualification testcoupons, QTCs, from the same heat of the low-alloy steel from which thebody was forged, may be normalized, austenitized, liquid quenched andtempered either simultaneously with or separately from the body forgingusing the same cycle temperatures and times. One of the QTCs may betempered at a temperature and time necessary to develop the mechanicalproperties required by the material specification. The remaining QTC maybe finish tempered along with the selectively reinforced BOP. These QTCsmay then be sent to a mechanical testing laboratory for mechanicaltesting of the mechanical properties to ensure that the base materialand the clad material meet the specified requirements.

Finish tempering the BOP body in this manner may allow the base materialand the clad material to meet the desired properties, including yieldstrength, hardness, and/or the requirements of NACE for resistance tostress corrosion cracking. Moreover, the CRA inlays should be moreresistant to and help reduce axial or bending fatigue failures.

For example, Grade F22 forgings or castings may be produced and machinedin the manner is which they have normally been produced, as describedabove. However, the heat treatment may be modified. The normalizing andaustenitizing temperature cycles and times along with the liquid quenchmay remain unchanged. The tempering temperature may be changed tobetween 900° F. (482° C.) and 1100° F. (593° C.) and the time attemperature may be reduced or remain unchanged. The forged BOP body maythen be selectively reinforced with INCONEL 725 or another agehardenable alloy or CRA.

Once the welding operations are complete, the selectively reinforced BOPbody may be charged to a heat treating furnace to perform a finishtemper that may be a combination temper, aging, and PWHT, to stressrelief anneal the HAZ of the Grade F22 base metal and age harden theINCONEL 725 CRA weld metal inlay and develop the mechanical propertiesof the Grade F22 forging. Other age hardenable alloys and/or CRAs, suchas, INCONEL 718 SPF (Alloy 718), may also be used as the filler metalfor this application. The temperature and time of the finish temper(combination temper/PWHT/age hardening heat treatment) step may bedetermined by the weld procedure qualification record (“PQR”) anddocumented on the weld procedure specification (“WPS”). After the finishtemper has been completed, a similarly processed QTC may be delivered toa metallurgical testing laboratory for the determination of themechanical properties of the material and whether they meet therequirements of the material specification.

Since the PWHT and the tempering cycle may be performed simultaneouslywith the age hardening of the clad inlay metal, there will not be anyloss of mechanical properties of the base metal as may occur where aseparate PWHT is performed after the temper of the low-alloy steel basemetal.

In an exemplary embodiment, a ram BOP body forging is produced from F22alloy. The raw forging is normalized at 1750° F. for 30 minutes per inchof CST “dwell” time, plus one hour “soak” time. It is then waterquenched and snap-tempered at 900° F. for 30 minutes per inch of CST,plus one hour.

Optionally, the quenched and snap-tempered ram BOP body is then roughmachined, for example with “weld necks” to facilitate welding flanges tothe BOP body. Optionally, various appurtenances such as flangeconnection or fixtures are then welded to the Q&ST body; theseappurtenances may preferably also be comprised of Q&ST F22 alloy. TheQ&ST body is then finished-machined and inlaid with INCONEL 725 in areasrequiring selective reinforcement and/or improved corrosion resistance.Optionally, the inlaid areas are further machined. Finally, thefinish-machined body with inlay reinforcement is “finish tempered” at1220° F. for a “dwell” time of about 40-42 minutes per inch of CST, plusa “soak” time of one hour. Following this procedure, the yield strengthof the F22 base material will be about 85,000 psi, and the yieldstrength of the inlaid INCONEL 725 will be greater than 115,000 psi.Additionally, the finish tempering process will also serve to relievethe residual stresses in the heat-affected zones of the welds, so thereis no need for supplemental PWHT.

In another exemplary embodiment, an annular BOP body may be fabricatedfrom ring forgings of 8630 Modified which have been quenched andsnap-tempered to about 900° F. at 30 minutes per inch of criticalsection “dwell” time plus one hour “soak” time. The Q&ST rings may bestacked together and full-penetration welded end-to-end. The weldedstack of Q&ST rings may be machined and selectively reinforced withINCONEL 725 weld inlay material, then finish tempered at about 1260° F.for a dwell time of about 30-45 minutes per inch of CST dwell time, plusa soak time of about one hour.

Embodiments and methods disclosed herein may advantageously provide forgenerating and analyzing oilfield component models with FEA using stressand/or fatigue analysis to determine the component's response underfatigue loading conditions characterized by large amounts of stress. Theresulting analysis may then be used to enhance component design,improving the performance of the component under fatigue loadingconditions.

Advantageously, embodiments disclosed herein may provide a method toestablish an overall oilfield component design based on ASMESection-VIII Div-3 or similar high-pressure, high-temperature equipmentdesign guidelines. The component may satisfy NACE peak stress and lifecycle requirements. Methods and embodiments disclosed herein may providefor oilfield components with an increased working lifespan. For example,the oilfield component may be modeled with simulated fatigue loadingconditions of repeated compression, bending, etc., to determine designfeatures that may extend the working lifespan of the oilfield component.

Advantageously, embodiments disclosed herein may provide a method tomanufacture oilfield components that is less costly than attempting tomanufacture the component from a solid, high strength corrosionresistant alloy or other metal that may meet the requirements of NACEMR0175. This is especially true in view of the fact that the mechanicalstrength of the body beneath the clad layer 0.250 to 0.500 inches fromthe well bore fluid wetted surfaces may be much lower that that requiredwithin that localized zones subject to fatigue failure. Otherembodiments may provide for the enhancement of existing componentdesigns so that sulfide stress corrosion cracking or corrosion relatedlimit conditions may be met by selectively reinforcing the oilfieldcomponent with higher strength material suitable for use in an oil andgas environment.

The selection of the cladding alloy may be based on the increasedmechanical strength of the clad layer and may also be based on themetallurgical bond achieved between the clad layer and the substrate. Anadditional attribute of the clad layer may be the corrosion resistancethat the cladding alloy may contribute to the oilfield component.Another attribute of the clad layer is that any scoring or gouging ofthe interior surface of the component is not likely to extend below thedepth of the clad layer, thus allowing the clad layer to continue toprotect the low-alloy steel substrate on which it is deposited.Particularly, the clad layer may also continue to protect the componentfrom pitting corrosion often found in the cavities of oilfieldcomponents. Moreover, the repair of gouges in the clad layer may beeasier and less costly to perform than the repair of similar damage tothe low-alloy steel substrate.

In other aspects, embodiments disclosed herein may advantageouslyprovide for a method to manufacture selectively reinforced oilfieldcomponents. The method may include finish tempering the oilfieldcomponent at a selected time and temperature to temper the base materialand age harden the clad material used to form the selectively reinforcedoilfield component. In this manner, the method may advantageouslyprovide for developing the required properties of the base material,post-weld heat treatment of the weldment joint adjoining the basematerial and the clad material, and age hardening the clad material.

While the invention has been described with respect to a limited numberof embodiments, those skilled in the art, having benefit of thisdisclosure, will appreciate that other embodiments can be devised whichdo not depart from the scope of the invention as disclosed herein.Accordingly, the scope of the invention should be limited only by theattached claims.

1. A process to manufacture an oilfield component, the processcomprising: selectively reinforcing a base material with anage-hardenable clad material; and selectively heating at least a portionof the clad material such that it age-hardens and the base materialremains at less than the tempering temperature of the base material. 2.The process of claim 1, wherein the base material comprises a fullytempered forging.
 3. The process of claim 1, wherein the base materialcomprises a snap-tempered forging.
 4. The process of claim 3, furthercomprising finish tempering the oilfield component at a selected timeand at a selected temperature to temper the base material and age hardenthe clad material.
 5. The process of claim 1, further comprising activecooling at least a portion of the base material.
 6. The process of claim5, wherein the active cooling comprises contacting a heat exchangemedium with at least a portion of a surface of the base material.
 7. Theprocess of claim 6, wherein the heat exchange medium comprises at leastone of air and water.
 8. The process of claim 1, wherein the basematerial remains at least 50° F. below the tempering temperature of thebase material.
 9. The process of claim 1, wherein the base materialremains at least 75° F. below the tempering temperature of the basematerial.
 10. The process of claim 1, wherein the selectively heatingcomprises heating the clad material using ceramic electric heatingblankets.
 11. The process of claim 1, wherein at least a portion of asurface of the base material is maintained at a temperature of 100° F.or less during the selectively heating.
 12. The process of claim 1,wherein the clad material comprises a thickness of at least 0.5 inches.13. The process of claim 1, wherein the base material comprises at leastone of 4130 low-alloy steel, Grade F22 low-alloy steel, and Grade 8630Modified low-alloy steel.
 14. The process of claim 1, wherein the cladmaterial comprises at least one of INCONEL 725, Alloy 718, Alloy 625,and 17-4PH stainless steel.
 15. The process of claim 1, wherein the basematerial remains at or below 1180° F.
 16. The process of claim 1,wherein at least a portion of the clad material is selectively heated toa temperature between about 1250° F. and about 1400° F.
 17. The processof claim 1, wherein the selective heating results in the clad materialhaving a yield strength of at least 115 ksi and the base material havinga maximum Brinell hardness of
 237. 18. The process of claim 1, whereinthe oilfield component comprises at least one of a blowout preventerbody, a stress joint, a valve body, a wellhead, a choke valve, and asucker rod.
 19. A ram blowout preventer manufactured using the processof claim
 1. 20. A body of a ram blowout preventer, comprising: alow-alloy base material; a vertical bore through the body; a horizontalbore through the body intersecting the vertical bore; wherein at least aportion of the body is selectively reinforced with a clad material; andwherein the base material is heat treated by a process comprisingselectively heating at least a portion of the clad material such thatthe clad material age-hardens and the base material remains at less thanthe tempering temperature of the base material.
 21. The body of the ramblowout preventer of claim 20, wherein the body comprises a flange neckselectively reinforced with the clad material.
 22. The body of the ramblowout preventer of claim 20, wherein the body is selectivelyreinforced based upon a result of a finite element analysis.